1. Field of the Invention
The present invention relates to a method of automatically tracking and photographing celestial objects which enables the capture of a freeze-frame picture of a celestial object(s) in long exposure astrophotography, and further relates to a camera employing this method.
2. Description of the Related Art
If long exposure astrophotography is carried out with a fixed camera, added light of stars during a long exposure form straight or curved light trails in the captured image, since celestial objects move relative to the camera due to the earth's rotation (diurnal motion). To carry out a long exposure in order to photograph a celestial object so that the celestial object appears to be still (stationary) relative to a photosensitive film or an image sensor (image pickup device), an equatorial equipped with an auto tracking system is generally used.
In recent years, a method of obtaining a still image of celestial objects such as planets and stars in long exposure astrophotography has been proposed in which a celestial object(s) is photographed a plurality of times with a fixed digital camera without using an equatorial, and thereafter, the images thus obtained at the plurality of times are added while correcting the positions of the celestial object(s) using data on the obtained images (see Japanese Unexamined Patent Publications Nos. 2006-279135 and 2003-259184).
However, an equatorial equipped with an auto tracking system is generally expensive, heavy and difficult to handle; in addition, it is essential to carry out a polar alignment procedure in which the polar axis of the equatorial is brought into alignment with the Pole Star (regarded as substantially the same as the North Celestial Pole (NCP)). The type of digital camera (disclosed in Japanese Unexamined Patent Publications Nos. 2006-279135 and 2003-259184) which synthesizes a plurality of images has inferior image registration accuracy and is slow in image processing speed, and therefore, it is practically impossible to synthesize a plurality of astronomical images using only such a type of digital camera while performing tracking astrophotography.